The present invention relates to composite sandwich structures of the type having a multicellular paper core intermediate and perpendicular facing sheets of linerboard, and more particularly, to a thermoformable composite construction in which an open-cell core is bonded to linerboards with a thermoplastic, to a preform, and to a method of making the construction from the preform.
Composite board sandwich structures with parallel liners and at least one corrugated paper medium have a wide variety of applications. Such elements may be used, for example, as lightweight, interior linings for walls, floors and ceiling panels, as facings, trims and headliners of automotive vehicles and for other applications where heat insulation, sound insulation and absorption and/or dampening of mechanical vibration is required. See, for example, U.S. Pat. No. 4,150,186, 4,170,674, 4,119,451, 4,093,482, 4,124,421, 4,184,905 and 4,242,399. The paper core in such prior art structures are typically adhered to the linerboard with an adhesive agent such as corn starch, PVA and EVA and, therefore, the structures are not thermoformable. Curing temperatures for such structures usually range from 400 to 500 degrees Fahrenheit. One patent, U.S. Pat. No. 4,184,905, discloses a curved flute corrugated board that has a liner, and corrugated paper medium with flutes running parallel to the plane of the liner. A layer of thermoplastic resin is formed between the corrugated medium and the liner such that the corrugated medium is adhered to the inner surface of the liner along the peak of the ridges of the corrugations by the resin layer. Though thermoformable, the product is lacking in bending, torsional, unilateral and compression strength and does not have good acoustic capabilities.
An open cell structure, i.e., a sandwich construction with cells open perpendicularly toward the surface of the liner, is disclosed in U.S. Pat. No. 4,479,992 but this construction is not thermoformable.